Power-assisted movable rack system

ABSTRACT

The invention provides a relatively simple and inexpensive power-assisted movable rack system, movement of which is controlled by an operator. The movable rack system comprises a plurality of movable racks, each of which includes a plurality of wheels, a DC motor turning forward or backward and reciprocating the movable rack, a pair of direction switches provided at opposite positions in moving directions of the movable rack, and an actuating circuit rotating the DC motor in one direction during the operation of one of the direction switches and rotating the DC motor in an opposite direction during the operation of the other direction switch. The DC motor applies dynamic braking force, so that movable racks can be stopped with a short braking distance.

FIELD OF THE INVENTION

This invention relates to a power-assisted movable rack system which ismanually operated with movable racks activated by electric motors usinga simplified circuit.

DESCRIPTION OF THE RELATED ART

In the related art, movable racks are moved by wheels attached thereon.When a plurality of such movable racks are arranged, a work space can beformed only in front of a movable rack to or from which articles are tobe loaded or unloaded while the remaining racks can remain in aconglomerated state. Therefore, the movable racks are very effective instoring articles in a limited space.

The existing movable racks are classified into those which are manuallymoved by an operator, those which are moved using a rotary handle forrotating wheels, and those which are driven by electric motors.

The purely manual type movable racks are used in a small scale, so thatthe rotary handle type movable racks and power-driven movable racks areusually in wide use.

With the rotary handle type movable racks, rotating force of the rotaryhandle is transmitted to the wheels via a transmission system having aspeed reduction gear train. Therefore, relatively large movable rackscan be moved by the operator. Further, a plurality of movable racks canbe moved by turning a rotary handle of only a single movable rack.However, a considerable amount of force is required in order to movevery large movable racks. Recently, a number of such movable racks havebeen widely used in libraries or the like, so that they are frequentlymoved by female workers who are considered to be weaker than maleworkers, which is very burdensome to female workers.

Conversely, the power-driven movable racks are provided with electricmotors depending upon their sizes, and can be easily operated by femalesand males. However, such power-driven movable racks suffer from thefollowing problems. It is assumed here that a command is issued in orderto form a work space between certain movable racks. Movable racks to bemoved and their moving directions should be calculated on the basis of aposition of a proposed work space and a position of a space to which themovable racks can be moved. Thereafter, it is necessary to determineelectric motors to be activated and rotating directions of the electricmotors. This means that complicated software is required for a controlcircuit or for controlling the electric motors. Further, if individualmovable racks have no available spaces to which they should move, it isnecessary to detect such a state and to stop them. Still further, if anyperson or article is detected in the spaces to which the movable racksare being moved, the movable racks have to be stopped. Finally, in orderto secure safety and protect the electric motors, a variety of detectioncircuits and control circuits should be provided, which inevitably makesthe power-driven movable racks rather expensive than the rotary handletype movable racks.

From another viewpoint, each movable rack is usually moved on straightguide rails which are usually approximately one meter long at most. Amaximum moving speed is approximately 4 km/h, which is substantiallyequal to a walking speed of the man. Although the movement of themovable racks is simple, the power-driven movable racks have to becontrolled in a complicated manner, and should have a complicatedcircuit configuration or software. This means that the power-drivenmovable racks are very expensive. Further, the power-driven movableracks are so slow that they take approximately 16 seconds in order toform a work space having a length of 900 mm to 1,000 mm while the rotaryhandle type movable racks of the related art take approximately 8seconds. This inevitably reduces the work efficiency of the power-drivenmovable racks.

The inventor has proposed in Japanese Patent Application No. 11-136,932a power-assisted movable rack, which comprises a rotary handle, a powertransmission mechanism for transmitting rotary force of the rotaryhandle to wheels, and electric motors for applying rotary force to thewheels when torque applied to the rotary handle becomes larger than apredetermined value.

The foregoing power-assisted movable rack looks like a rotary handletype movable rack, but can be moved with small rotary force whenassisted by an electric motor even if the movable rack is very heavy.

It is therefore a first object of the invention to provide apower-assisted movable rack system which is designed on the basis of thetechnical concept of the related art, is moved under the control of anoperator, and includes a simple and inexpensive control circuit.

A second object of the invention is to provide a power-assisted movablerack system which can be moved speedily, reduce a standby time whenforming a work space and improve work efficiency.

It is a third object of the invention to provide a power-assistedmovable rack system in which a plurality of movable racks can bespeedily moved at the same time in order to form a work space.

A fourth object of the invention is to provide a power-assisted movablerack system which can be quickly stopped even when articles are heavilyand not uniformly loaded.

Finally, the invention is intended to provide a power-assisted movablerack system in which a normal stop and an emergency stop of movableracks can be distinguished, and in which an emergency stopping distancecan be reduced compared with a normal stopping distance.

SUMMARY OF THE INVENTION

The invention provides a power-assisted movable rack system comprising aplurality of movable racks. Each of the movable rack includes: aplurality of wheels; a DC motor turning forward or backward andreciprocating the movable rack; a pair of direction switches provided atopposite positions in moving directions of the movable rack; and anactuating circuit rotating the DC motor in one direction during theoperation of one of the direction switches and rotating the DC motor inan opposite direction during the operation of the other directionswitch.

An operator can move movable racks in opposite directions by operatingdirection switches as he or she desires.

The DC motor functioning as a drive source has a maximum start torqueand can activate movable racks with a reduced speed reduction ratio, sothat movable racks can be moved at a high speed. Further, the DC motorcan apply maximum dynamic braking to movable racks, which enables themovable racks to stop with a short braking distance.

Further, the invention provides a power-assisted movable rack, whichcomprises a plurality of movable racks, each of which includes: aplurality of wheels; a DC motor turning forward or backward andreciprocating the movable rack; a pair of right and left directionswitches provided at opposite side edges in moving directions of themovable rack; and an actuating circuit rotating the DC motor in onedirection during the operation of the right direction switch for thepurpose of moving the movable rack to the right, and rotating the DCmotor in an opposite direction during the operation of the leftdirection switch for purpose of moving the movable rack to the left. Themovable racks are juxtaposed. One movable rack is capable of movingother movable racks; a signal transmitter is included for sending arightward signal to a right driven movable rack when the right directionswitch is operated on a driving movable rack, and sending a leftwardsignal to a left driven movable rack when the left direction switch isoperated on the driving movable rack; and the actuating circuit providespower to the right or left driven movable rack receiving the rightwardor leftward signal, the power being smaller than power applied to thedriving movable rack.

In a movable rack where either the left or right direction switch isoperated, the DC motor associated with the operated switch is actuatedin order to move the movable rack (functioning as a driving movablerack) to the left or right. A movable rack which is left or right to thedriving movable rack is also moved. Power which is smaller than thatapplied to the driving movable rack is applied to the movable rack movedby the driving movable rack, so that running torque is generated in themovable rack moved by the driving movable rack. This is effective inreducing loads applied to the DC motor functioning as a drive source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a power-assisted movable rack systemincluding a plurality of movable racks according to a first embodimentof the invention.

FIG. 2 is a side elevation showing how one of movable racks is movedwhen a direction switch is operated thereon.

FIG. 3 is a side elevation schematically showing the concept of safetybars and buffers provided in the power-assisted movable rack system.

FIG. 4 is a side elevation of an example of the buffers.

FIG. 5 is a top plan view of the buffer.

FIG. 6 is a front elevation of the buffer.

FIG. 7 shows an external appearance of a power-assisted movable rack ina second embodiment of the invention.

FIG. 8 shows an external appearance of a power-assisted movable rack ina third embodiment of the invention.

FIG. 9 shows an example of a circuit applicable to the invention.

FIG. 10 shows a circuit of a safety device which is applicable to theinvention and includes safety bars and buffers.

FIG. 11 is a circuit diagram of the safety device, depicted in asimplified manner.

FIG. 12 shows a circuit for selectively moving movable racks forward orbackward.

FIG. 13 shows a further control circuit applicable to the invention.

FIG. 14 is a flowchart showing the operation of the power-assistedmovable rack system including the foregoing control circuit.

FIG. 15 shows a power supply circuit applicable to the invention.

FIG. 16 shows a further power supply circuit applicable to theinvention.

FIG. 17 shows an external appearance of a power-assisted movable rackssystem including a plurality of movable racks in another example of theinvention.

FIG. 18 shows a further control circuit applicable to the invention.

FIG. 19 is a side elevation of a switch applicable to the invention.

FIG. 20 is a top plan view of the switch shown in FIG. 19.

FIG. 21 shows a brake circuit applicable to the invention.

FIG. 22 is a bottom plan view of the movable rack, showing a wheelmoving mechanism.

FIG. 23 is a flowchart showing a braking operation in the power-assistedmovable rack system.

FIG. 24 is a flowchart showing a further braking operation in thepower-assisted movable rack system.

FIG. 25 is a flow chart showing a still further braking operation in thepower-assisted movable rack system.

FIG. 26 is a graph showing the relationship between stopping distancesand weight of load when the movable rack systems include the brakingdevice of the related art and the braking device of the invention.

DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the preferredembodiments shown in the accompanying drawings. Referring to FIG. 1,movable racks 1 to 5 are provided with wheels 14, 24, 34, 44 and 54, andelectric motors 13, 23, 33, 43 and 53, respectively. The electric motors13, 23, 33, 43 and 53 are used to turn the wheels 14, 24, 34, 44 and 54,which run on rails laid on a floor.

In an example of FIG. 1, frontages of each movable rack through whicharticles are loaded or unloaded are at right angles to the plane of thedrawing sheet of FIG. 1, so that the movable racks are moved in thedirection which is at right angles to the front surfaces thereof (i.e.to the left or right in parallel to the plane of FIG. 1). In thisspecification, the frontages of individual movable racks are either afront or rear surface thereof, while the vertical faces at right anglesto the frontages are side surfaces, which are visible in FIG. 1.

The electric motors 13, 23, 33, 43 and 53 are DC motors which canproduce maximum torque when they are activated. The rotating directionsof these motors are reversed by changing polarities of a DC current tobe supplied, so that the movable racks move forward or backward inaccordance with rotating directions of the wheels. Further, the electricmotors generates a permanent magnetic field using permanent magnets.Each movable rack is provided with a pair of direction switches atleading and trailing edges thereof, i.e. on a side panel on the sidesurface thereof. Specifically, the movable rack 1 has direction switches11 and 12; the movable rack 2 has direction switches 21 and 22; themovable rack 3 has direction switches 31, 32; and the movable rack 4 hasdirection switches 41 and 42; and the movable rack 4 has directionswitches 51 and 52.

Each movable rack is provided with an actuating circuit which suppliespower to each electric motor and turns it when one of the directionswitches is operated. For example, when the direction switch 11, 21, 31,41 or 51 is operated, DC power is supplied in order to turn the electricmotor 13, 23, 33, 43 or 53 in a first direction. Further, when thedirection switch 12, 22, 32, 42 or 52 is operated, the DC power issupplied in order to turn the electric motor 13, 23, 33, 43 or 53 in asecond direction opposite to the first direction.

The electric motors 13, 23, 33, 43 and 53 include clutches, or clutchesare provided in power transmission mechanisms between these motors andthe wheels 14, 24, 34, 44 and 54. The clutches are connected to electricmotors which are in operation, and transmit rotary force of the motorsto the wheels. Otherwise, the clutches are disconnected from theelectric motors which remain inactive. Alternately, the clutches may beelectromagnetic clutches which are activated when the electric motorsare turned on, or centrifugal clutches which are connected by thecentrifugal force when the electric motors are activated and turned.

Referring to FIG. 1, when the left direction switch 31 is pushed to theright on the movable rack 3, its electric motor 33 turns in onedirection, which enables the movable rack 3 to be moved to the right. Asa result, a work space is formed between the movable racks 2 and 3. Inthis case, only the electric motor 33 of the movable rack 3 is activatedand is connected to the clutch of the movable rack 3, so that the rotaryforce of the electric motor 33 is transmitted to the wheels 34. In thisstate, no power is supplied to the electric motors of the movable racksexcept for the movable rack 3, so that the clutches of those motorsremain disconnected. The other movable racks can be moved withrelatively small force since their wheels have a reduced rotationresistance. Therefore, the movement of the movable rack 3 in response tothe activation of the electric motor 33 allows the movable racks 4 and 5to move to the right.

The movable rack 3 keeps on moving while the direction switch 31 isbeing pushed. Referring to FIG. 2, the movable rack 3 is moved to theright as shown by a chain line 3A and a dashed line 3B. When an operatorconsiders that there is a sufficient work space between the movableracks 2 and 3, he or she releases the direction switch 31 in order tostop the movable rack 3. As a result, the movable racks 4 and 5 movedtogether with the movable rack 3 are also stopped.

If the right direction switch 32 of the movable rack 3 is pushed to theleft, the movable rack 3 is moved leftward. The movable rack 3 stopswhen the direction switch 32 is released. The foregoing operations areapplied to all of the movable racks. In other words, when each leftdirection switch is pushed to the right, each movable rack is moved tothe right. On the other hand, when each right direction switch is pushedto the left, each movable rack is moved to the left. As soon as eachswitch is released, each movable rack is stopped at its currentposition.

In the example shown in FIG. 1, the five movable racks can be gatheredas one group, and can be individually moved in order to form a workspace between desired movable racks. Sometimes, the outermost movablerack 1 or 5 has to move other movable racks which are disconnected fromtheir clutches. Therefore, the electric motor of each movable rack isrequired to have torque enough to move movable racks that aredisconnected from their clutches.

Electric motors of existing movable racks are usually AC motors havinglow running torque, so that the electric motors of all the movable racksto be moved are simultaneously activated in order to compensate for thelow torque.

According to the invention, the electric motor of only one movable rackis activated in order to push other movable racks. This can simplify thecircuit configuration. The electric motors should have large torque,i.e. running torque, so that DC motors having large running torque areused in the invention.

The outermost movable racks are often required to move many movableracks while the intermediate movable rack pushes a relatively reducednumber of movable racks. As a result, the electric motors of theoutermost movable racks may have relatively large torque while theelectric motors of inner movable racks may have relatively small torque.

In this embodiment, the movable racks include the direction switches ontheir opposite side edges. The right or left direction switches areselectively operated in order to move movable racks to the right or leftas if the operator manually moves the movable racks by himself orherself. The movable racks are actually moved by the assistance of theelectric motors, so that heavy movable racks can be moved easily andsmoothly.

Only during the depression of the direction switches, power is suppliedto the electric motors in order to move the movable racks. When thedirection switches are released, the movable racks are stopped. Themovable racks are selectively moved to the right or left depending uponwhich left or right direction switches are operated by the operator. Inother words, the movable racks are moved in a desired direction undercontrol of the operator. Therefore, it is possible to dispense withvarious detection circuits which are necessary in existing power-drivenmovable racks in order to check the following items: a position of anexisting work space; a position of a new work space to be formed; and adirection to move movable racks on the basis of the existing work spaceand the new work space. Further, it is possible to dispense with controlcircuits which are operated in accordance with data obtained by theforegoing detection circuits. As a result, the present invention canprovide the power-assisted movable racks which have the simple circuitconfiguration and are less expensive.

The power-assisted movable racks are operated under operator's control.When an operator is aware that someone is present in an existing workspace, he or she never moves movable racks in a direction where theexisting work space will be narrowed. However, an operator who isunaware of someone behind a movable rack may move movable racks andnarrow the existing work space. In such a case, the movable racks arestopped by inactivating the electric motors.

Referring to FIG. 3, a safety device will be described with respect tothe movable racks 1, 2 and 3, for example, in order to simplify thedescription. The safety device includes safety bars 15, 16, 25, 26, 35and 36, which are positioned on the front and rear surfaces of themovable racks 1, 2 and 3, and come into contact with operators or otherarticles. Specifically, the movable rack 1 has the safety bars 15 and16; the movable rack 2 has safety bars 25 and 26; and the movable rack 3has safety bars 35 and 36. Each safety bar laterally extendssubstantially along the width of each movable rack, and has a safety barswitch which is activated when something or the operator comes intocontact therewith. The safety bars may be attached using any material,e.g. they may be laterally supported using a front panel, supportpillars or the like. When any safety bar switch is activated, powersupplied to the electric motors will be immediately suspended. As shownin FIG. 3, the safety bars are near the bottoms of the movable racks.Alternatively, they may be present at higher positions of the movableracks, or both at the bottoms and higher positions of the movable racks.

In the movable rack system, the movable racks can be moved inpredetermined distances. In the example of FIG. 3, end stops 61 and 62are used in order to regulate moving distances of the movable racks 1and 3. When coming into contact with the end stop 61, the movable rack 1is kept from moving further to the left. The end stop 62 prevents themovable rack 3 from moving further to the right. However, if the movablerack 1 or 3 is directly stopped by the end stop 61 or 62, articlesstored therein may become loose or fall down. In order to overcome thisproblem, a buffer 17 is provided near the left side edge of the leftmostmovable rack 1 in order to cooperate with the end stop 61 while a buffer37 is provided near the right side edge of the rightmost movable rack 3in order to cooperate with the end stop 62. The buffers 17 and 37alleviate shocks applied to the movable racks 1 and 3 when they strikeagainst the end stops 61 and 62, and also suspend the power supplied tothe electric motors and protect them against overload even if thedirection switches are left operated.

The buffer 17 will be described with reference to FIG. 4 to FIG. 6. Eachmovable rack is mounted on an under-frame 64. Alternatively, articlesmay be directly loaded on the under-frame 64. A plurality of steel beams65 in the shape of an E-channel are fixedly attached on an inner ceilingof the under-frame 64 by welding or the like. The beams 65 extend in themoving direction of the movable rack, and are appropriately spaced whenviewed in the direction of the frontage of the movable rack. The frontand rear wheels 14 are rotatably attached to the bottom of the beams 65via pillow blocks 66. The front and rear wheels 14 are placed and turnon rails 80, which enables the movable rack to move on the rails 80. Thefront or rear wheels 14 are activated and turned by the electric motor.

An L-shaped angle member 67 is attached on the bottom of the beams 65and between the front and rear wheels 14 with spaces maintainedtherebetween. A bearing 68 in the shape of an inverted U is attached toan underside of the angle member 67, and extends along the length of thebeam 65. Two shafts 69 are fixedly attached via holes in front and reardownward pieces, and are parallel to each other. A contact member 70associated with the end stop 61 is fitted on outer surfaces of theshafts 69, extends over the shafts 69, and is slidable on the shafts 69.The contact member 70 has a part of its lower part extending downward,which comes into contact with the end stop 61. The end stop 61 is madeof an angle member in the shape of letter L, and includes horizontalpieces fixedly attached on the floor and vertical pieces extendingupward from the horizontal pieces. The vertical pieces come into contactwith the contact member 70.

A compressed coil spring 71 is fitted around the two shafts 69. Aresiliency of the compressed coil spring 71 acts between the rightvertical piece of the bearing 68 and the contact member 70, urges thecontact member 70 to the left. The contact member 70 comes into contactwith the left vertical piece of the bearing 68, thereby preventing thecontact member 70 from being moved by the resiliency of the coil spring71. Referring to FIG. 4, when the movable rack 1 is moved to the left,the contact member 70 comes into contact with the end stop 61, and ismoved to the right while compressing the coil spring 71. As a result,force for returning the coil spring 71 is stored.

The bearing 68 includes an end switch 73, and the contact member 70 hasan end switch actuator 72 on its top. The end switch 73 has a tip of itsoperation lever placed on the end switch actuator 72. The end switchactuator 72 extends in a sliding direction of the contact member 70, andhas a sloped part 75 at the center thereof. The end switch actuator 72has different heights at the opposite sides of the sloped part 75.Normally, the contact member 72 is in contact with the left verticalpiece by the resiliency of the coil spring 71, and the tip of theoperation lever of the end switch 73 is present on a lower side of theend switch actuator 72, so that the end switch 73 does not operate.

The contact member 70 comes into contact with the end stop 61 and movesto the right (see FIG. 4) against the resiliency of the coil spring 71.In this state, the contact member 70 and the end switch actuator 72 aremoved to the right, so that the sloped part 75 of the end switchactuator 72 pushes the tip of the operation lever upward. As a result,the end switch 73 will be activated, and power supplied to the DC motorof the movable rack will be suspended.

The buffer 17 is effective in the following respect: when the movablerack 1 is moved to its limit, the contact member 70 strikes against theend stop 61, and is urged to move against the resiliency of the coilspring 71, so that shocks applied by the movable rack 1 stopped by theend stop 61 is absorbed by the coil spring 71, and the articles storedon the movable rack 1 are prevented from becoming loose or falling down.The coil spring 71 absorbs the shocks, is compressed, and urges themovable rack 1 backward using the force stored therein. In this state,the end switch 73 is released. The power will be re-supplied to theelectric motors by operating one of the direction switches on themovable racks.

The buffer 37 shown in FIG. 3 is identical to the buffer 17 althoughtheir orientations are reverse.

An electric circuit applicable to the foregoing embodiment will bedescribed with reference to FIG. 9 to FIG. 12. FIG. 9 shows a powersupply circuit for an electric motor of one of the movable racks. Inthis drawing, reference number 81 denotes a DC stabilizing power supplyfor converting AC power to DC power, and reference number 82 denotes acontactor for selecting a contact to be conducted by changing a polarityof the supplied DC power. A rightward switch SW1R relates to the leftdirection switch of each movable rack, and a leftward switch SW1Lrelates to the right direction switch of each movable rack, as shown inFIG. 1.

Referring to FIG. 9, the contactor 82 includes a plurality of contactswhich are operated when the DC power is supplied in one direction, and aplurality of contact which are operated when the DC power is supplied inthe reverse direction. These contacts are symmetrical. When therightward switch SW1R is turned on, the DC is supplied from the positivepole of the DC stabilizing power supply 81 via right contacts 21, 22 andleft contacts A1/a, A2/b of the contactor 82, rightward switch SW1R, abreak contact of a relay RL1, and the negative pole of the DCstabilizing power supply 81. Specifically, the contacts at the left halfin FIG. 9 are activated. Thereafter, the DC power is supplied from thepositive pole of the DC stabilizing power supply 81 via left contacts Rand U of the contactor 82, a motor M, contacts W and T, a break contactof the relay RL1, and the negative pole of the DC stabilizing powersupply 81. As a result, the motor M is turned in one direction (i.e.forward in this example), so that the movable rack is moved to the right(in FIG. 1).

When the leftward switch SW1L is turned on, the DC power is suppliedfrom the positive pole of the DC stabilizing power supply 81 via leftcontacts 21, 22 and left contacts A1/a, A2/b of the contactor 82, theleftward switch SW1R, the break contact of the relay RL1, and thenegative pole of the DC stabilizing power supply 81. Specifically, thecontacts at the right half in FIG. 9 are activated. Thereafter, the DCpower is supplied from the positive pole of the DC stabilizing powersupply 81 via right contacts R and U of the contactor 82, the motor M,contacts W and T, a break contact of the relay RL1, and the negativepole of the DC stabilizing power supply 81. As a result, the motor M isturned in the reverse direction, so that the movable rack is moved tothe left.

Regardless of the moving direction, right or left, of the movable rack,the DC power supplied to the contactor 82 is suspended by releasing thedirection switch of the movable rack and turns off either the switchSW1R or SW1L, so that the contacts of the contactor 82 to supply the DCpower to the motor M will be moved to the neutral position. Therefore,the motor M will be stopped, and the movable rack becomes stationary.

FIGS. 10 and 11 show the relationship between the safety bars and theend switches shown in FIG. 3. In these figures, ELB denotes an earthleakage breaker, PS denotes a DC stabilizing power supply, ESL denotes aleft end switch, ESR denotes a right end switch, SB1, SB2, and SB3denote safety bar switches of the movable racks 1, 2 and 3, and RL1, RL2and RL3 denote relays of the movable racks 1, 2 and 3. These switcheshave break contacts. The relays RL1, RL2 and RL3 are connected inparallel, while the switches ESL, SB1, SB2, SB3 and ESR are connected inseries. Therefore, the relays are continuously energized, and will bede-energized when any one of the foregoing switches is turned on andthen turned off.

FIG. 12 equivalently shows circuits for introducing power to theelectric motors of the respective movable racks. The contactors of themovable racks include electromagnets M1L, M1R, M2L, M2R, M3L and M3R.Letters L and R in these reference numerals denote the directions of theDC power because it is supplied in the forward and backward directions.For example, in the movable rack 1, the contact of the relay RL1, theleftward switch SW1L and the electromagnet M1R which are connected inseries are connected to the DC power supply, and the rightward switchSW1R and the electromagnet M1L which are connected in series areconnected to the DC power supply. In the movable rack 2, the contact ofthe relay RL2, the leftward switch SW2L and the electromagnet M2R whichare connected in series are connected to the DC power supply, and therightward switch SW2R, the leftward switch SW2L and the electromagnetM2L which are connected in series are connected to the DC power supply.The same holds true to the movable rack 3.

As described with respect to FIGS. 10 and 11, when any of safety barswitches or the end switches is actuated, the relays RL1, RL2 and RL3will be de-energized, so that the contacts of the relays shown in FIG.12 will be opened. As result, power supplied to the movable rack whereeither right or left direction switch is turned on will be suspended, sothat no power is supplied to the electric motor, thereby stopping themovable rack. The DC power supplied to the contactor 82 shown in FIG. 9is suspended, the contacts of the contactor 82 are opened, the electricmotor will not receive any DC power, and the movable rack will bestopped.

According to the invention, the power-assisted movable racks has thesimplified circuit configuration which enables the operator to controlthe movement of the movable racks as desired. Even if the operator isunaware of the presence of a person in an existing work space andhappens to move movable racks to narrow the work space, the safety barswitches will be operated in order to suspend power supply to themovable racks and stop them. Further, when detecting that a movableracks strikes against the end stop, the end switch suspends power supplyto the movable rack and stops it. The safety bar switches and the endswitches are preferably connected in series. Even when these switchesare provided, the circuit configuration of the movable racks of thepresent invention is simplified compared with that of the movable racksof the related art.

In the foregoing embodiment, the clutches are provided between thewheels and electric motors of the movable racks, and remain disconnectedso long as the electric motors are not activated. However, the clutchesare not always indispensable for the following reasons. According to theinvention, the power-assisted movable rack system employs the DC motorsas the driving force supply. Having large running torque, the DC motorscan have a small speed reduction ratio, which means that the rotationalforce of the wheels is transmitted to the DC motors with a relativelysmall resistance. Even if no clutch is provided between the wheels andthe DC motors, only a relatively small load is required to move aplurality of movable racks via one movable rack. Therefore, the clutchesmay be dispensable. Further, the wheels may turn on the rails inresponse to an earthquake even when no clutches are provided. Noearthquake energy will be transmitted to the movable racks, which iseffective in protecting the movable racks against vibrations.

Needless to say, the clutches which are connected to the electric motorsand wheels only during the activation of the electric motors enable aplurality of movable racks to be smoothly moved by one movable rack.Further, the clutches are advantageous in protecting the movable racksagainst earthquakes.

The small speed reduction ratio realized by using the DC motors iseffective in moving the movable racks at high speeds, which enablesquick formation of a work space and improves the work efficiency of themovable rack system.

In the embodiment shown in FIGS. 1 to 3, the work space may be alsoformed between two movable racks facing with each other bysimultaneously moving them. For instance, it is assumed that a workspace is to be formed between the movable racks 2 and 3. The rightdirection switch 22 of the movable rack 2 is pushed to the left whilethe left direction switch 31 of the movable rack 3 is pushed to theright, so that the movable racks 2 and 3 moved to the left and right,respectively. Needless to say, the remaining movable racks may be alsomoved in this state. The work space can be quickly formed bysimultaneously moving movable racks at the opposite side thereof becauseof the accelerated movement of the movable racks enabled by the DCmotors. A 900 mm to 1,000 mm work space can be formed in approximatelyfour seconds.

However, if two movable racks are simultaneously moved to the left andright, respectively, one of them may have a reduced margin to move, andmake its buffer strike against the end stop. The following describe thecase in which the buffer 17 comes into contact with the end stop 61shown in FIGS. 4 to 6. In the buffer 17, the contact member 70 strikesagainst the end stop 61, and slides along the shaft 69 while compressingthe coil spring 71. The end switch actuator 72 moves with the contactmember 70, and the sloped part of the end switch actuator 72 pushes theoperation lever of the end switch 73, thereby operating the end switch73. Therefore, the motor activating circuits of all the movable rackswill be released, thereby preventing the motor of the movable rackstriking against the end stop from being overloaded.

If the end switch remains active in the foregoing state, no power willbe supplied to the DC motors, and no movable racks can be moved.However, the movable rack 1 striking the end stop is pushed back by thecompressed coil spring, which returns the end switch to its originalstate. As a result, the movable rack 1 can resume its movement. With thebuffers shown in FIGS. 4 to 6, the contact member 70 is pushed back bythe force stored in the coil spring 71, and presses the end stop 61, sothat the movable rack 1 is moved to the right as shown in FIG. 4.Further, the operation lever of the end switch 73 slides down on thesloped part 75 of the end switch actuator 72, thereby turning the endswitch 73 off. Thereafter, power can be supplied to the electric motorsof the movable racks, which enables the movable racks to be moved byoperating the direction switches.

In the example shown in FIGS. 1 to 3, the movable racks can be moved tothe right or left by operating the left or right direction switch to adesired direction in which a movable rack is to be moved. Alternatively,as shown in FIG. 7, a movable rack 8 is provided with a grip 81 at thecenter of its side surface, and is moved in a desired direction bypulling the grip 81 to the right or left. When the grip 81 is pulled tothe right, a rightward switch (not shown but corresponding to the switchSW1R shown in FIG. 9) is turned on, and a DC motor 83 of the movablerack 8 is rotated forward in order to move the movable rack 8 to theright. Conversely, when the grip 81 is pulled to the left, a leftwardswitch (not shown but corresponding to the switch SW1L shown in FIG. 9)is turned on, and the DC motor 83 of the movable rack 8 is rotated inthe reverse direction in order to move the movable rack 8 to the left.

With this structure, the movable rack 8 can be smoothly moved underassistance of the electric motor 83, so that the operator may feel as ifhe or she actually moves them by himself or herself by pulling the grip81. In this case, the end stops and the circuit configuration may beidentical to those in the foregoing example. This structure is asadvantageous and effective in the foregoing example.

Referring to FIG. 8, right and left grips 91 and 92 are provided nearthe opposite side edges of a movable rack 9 in order to move it in adesired direction. Specifically, when the grip 91 is pulled in order tomove the movable rack 9 to the left, a switch corresponding to theswitch SW1L (shown in FIG. 9) is turned on, and an electric motor 93 ofthe movable rack 9 is rotated in one direction, thereby moving themovable rack 9 to the left. Conversely, when the grip 92 is pulled inorder to move the movable rack 9 to the right, a switch corresponding tothe switch SW1R (shown in FIG. 9) is turned on, and the electric motor93 of the movable rack 9 is rotated in the reverse direction, therebymoving the movable rack 9 to the right.

With this structure, the movable racks can be smoothly moved by theassistance of the electric motor 83, so that the operator may feel as ifhe or she actually moves them by himself or herself by pulling the grip91 or 92. In this case, the end stops and the circuit configuration maybe identical to those in the foregoing example. This structure is asadvantageous and effective in the foregoing example.

The invention will be described with reference to a second embodimentusing a modified control circuit shown in FIG. 13. This control circuitincludes left direction switches which correspond to the left directionswitches 11, 21, 31, 41 and 51 shown in FIG. 1, and right directionswitches which correspond to the right direction switches 12, 22, 32, 42and 52 shown in FIG. 1.

In FIG. 13, reference numeral 120 denotes a circuit board incorporatedin each movable rack. A circuit board 120 of a first movable rackincludes terminals 121, 122, 123 and 124 to be connected to a circuitboard 120 of a second movable rack which is left to the first movablerack, and terminals 131, 132, 133 and 134 to be connected to the circuitboard of the second movable rack which is right to the first movablerack. The terminal 121 is used to receive DC 24V power from anappropriate power supply and is connected to the terminal 131. Theterminal 124 is a grounding terminal connected to the terminal 134. Eachcircuit board 120 includes a central processing unit (called the “CPU”)150, a DC-DC converter 153 and an actuating circuit 154. The actuatingcircuit 154 supplies DC power to and rotates a DC motor 152 forward orbackward under the control of the CPU 150. The DC-DC converter 153converts a voltage of the DC 24V power to a voltage appropriate for theCPU 150 and maintains it in a stable state. Further, the DC-DC converter153 receives DC 24V power from an AC-DC converter 155 which converts ACpower to DC power.

Each CPU 150 is connected to a right direction switch 104, a leftdirection switch 106, and an emergency stop switch 156. The emergencystop switch 156 may be a switch which is manually operated at the timeof emergency, or may be a switch which is positioned on the frontage ofeach movable rack and is turned on whenever it comes into contact withan operator or something.

It is assumed here that a right direction switch 104 is turned on a(driving) movable rack and that the driving movable rack is used to movea (driven) movable rack which is adjacent to the driving movable rack.The CPU 150 of the driving movable rack controls the actuating circuit154, drives the DC motor 152 in order to move the driving movable rackto the right and issues a rightward signal at the same time. Therightward signal is sent from the terminal 133 to a circuit board 120 ofthe driven movable rack, which is right to the driving movable rack, viathe terminal 123. On the other hand, when a left direction switch 106 isactivated on the driving movable rack, the CPU 150 of the drivingmovable rack controls the actuating circuit 154, actuates the DC motor152 in order move the driving movable rack to the left, and issues aleftward signal at the same time. The leftward signal is sent from theterminal 122 via the terminal 132 to the circuit board 120 of the drivenmovable rack which is left to the driving movable rack.

When receiving a leftward signal from the driving movable rack via theterminal 132, the CPU 150 of the driven movable rack controls theactuating circuit 154, actuates the electric motor 152 in order to movethe driven movable rack to the left, and issues and transmits theleftward signal to another driven movable rack which left to the drivenmovable rack, via the terminal 122. Conversely, when receiving arightward signal from the driving movable rack via the terminal 123, theCPU 150 controls the actuating circuit 154, actuates the electric motor152 in order to move the driven movable rack to the right, and issuesand transmits the rightward signal to the driven movable rack which isright to the driven movable rack, via the terminal 133.

Further, the CPU 150 controls the actuating circuit 154 in order tooperate the DC motor 152 of the driving movable rack, where the right orleft direction switch 104 or 106 is operated, at a rated output.

When receiving the rightward or leftward signal from the driving movablerack, the CPU 150 of the driven movable rack controls the actuatingcircuit 154 so that the actuating circuit 154 provides the DC motor 152of the driven movable rack with power which is smaller than thatsupplied to the driving movable rack (e.g. power which is barelysufficient for the driven movable rack to move by itself), or powerwhich enables the driven movable rack to move by itself at a speed whichis lower than a moving speed of the driving movable rack. The ratedoutput of the DC motor 152 is obtained by supplying a 6 A-24V current,so that the power by which the driven movable rack can move by itselfcan be obtained by supplying an approximately 2 A-24V current.

The circuit boards in the individual movable racks are identicallystructured. For example, when the right direction switch 104 of adriving movable rack is operated, the rightward signal will be issuedand transmitted to a driven movable racks which is right to the drivingmovable rack via the circuit board 120. When the left direction switch106 of the driving movable rack is operated, the rightward signal willbe issued and transmitted to a driven movable rack which is left to thedriving movable rack via the circuit board 120.

The operation of the second embodiment will be described with referenceto a flowchart of FIG. 14. An active or inactive state of the emergencystop switch 156 is checked (step S2) while the movable racks arestationary (step S1). When the emergency stop switch 156 remainsinactive, it is checked (step S3) whether or not the right switch 104 isactive. If the right direction switch 104 is active, an output currentis set to 6 A (step S4), and the DC motor 152 is actuated at the ratedoutput in order to move one of movable racks to the right (step S5).

If the right direction switch 104 remains inactive in step S3, it ischecked (step S6) whether or not the rightward signal has been receivedfrom a driving movable rack. If so, the output current is set to 2 A(step S7), and power which is not sufficient for a driven movable rackto move by itself but is enough to move the driven movable rack to theright is supplied to the electric motor 152.

When the rightward signal is absent in step S6, it is checked (step S8)whether or not the left direction switch 106 is active. When the leftdirection switch 106 is active, the output current is set to 6 A (stepS9), and the DC motor 152 is activated at the rated output in order tomove the driving movable rack to the left.

If the left direction switch is not active in step S8, it is checked(step S11) whether or not the leftward signal has arrived from thedriving movable rack. If the leftward signal is present, the outputcurrent is set to 2 A (step S12), and power which is not sufficient fora driven movable rack to move by itself but is enough to move the drivenmovable rack to the right is supplied to the electric motor 152.

When no leftward signal is present in step S1, control returns to thestep S2, and the foregoing steps are repeated.

A step may be added after the steps S4, S7, S8 and S12 in order to checkthe operation of the emergency stop switch 156 during the movement ofmovable racks and in order to disconnect the electric motor 152 from thepower supply.

As described so far, a plurality of power-assisted movable racks arejuxtaposed, and one movable rack can move other power-assisted movableracks. For example, when the rightward or leftward signal is transmittedfrom the driving movable rack to the driven movable rack, power which issmaller than that for moving the driving movable rack, e.g. the powerwhich is not enough for the driven movable rack to move by itself, issupplied to the DC motor of the driven movable rack. Therefore, in orderto move the driven movable rack, the driving movable rack is applied areduced load, which enables the driving movable rack to move many drivenmovable racks as possible. Even when a number of movable racks have tobe pushed by one movable rack, the work space having desired width canbe formed as quickly as possible.

The power supplied to the DC motors of the driven movable racks is madesmaller than the power supplied to the driving movable rack for thefollowing reasons. No space may be formed between movable racks when thedriven movable rack is positioned in front of the driving movable rackand is pushed forward by the driving movable rack. Therefore, the powerto be supplied to the DC motor of the driven movable rack is smallerthan that supplied to the driving movable rack (e.g. power which isbarely sufficient for the driven movable rack to move by itself), orpower which enables the driven movable rack to move by itself at a speedwhich is lower than a moving speed of the driving movable rack.

Usually each movable rack requires maximum energy when it is actuated.Once each movable rack starts moving, it requires reduced energy. Withdriven movable rack receiving the rightward or leftward signal from thedriving movable rack, the DC motor receives the power which is notsufficient enough to enable the movement of the driven movable rack byitself is supplied for a short period of time before the driven movablerack starts moving.

As shown in the circuit of FIG. 15, DC power supply circuits areprovided for individual movable racks, receive commercial AC power, andconvert it to DC power. Further, the DC power supply circuits 160 areconnected in parallel, so that the DC power supply of one movable rackmay supply power to the DC motors of other movable racks.

The foregoing structure of the power-assisted movable rack system canprotect the DC power supply circuit 160 of one movable rack againstoverload when the movable rack is used to push other movable racks. TheDC power supply circuit 160 can receive power from DC power supplycircuits 160 of other movable racks. Therefore, each DC power supplycircuit 160 can have a small capacity, so that the circuits of themovable rack system can be made light in weight and less expensive.Further, if the DC power supply circuit 160 is provided for each blockconstituted by a plurality of movable racks, it should have a relativelylarge capacity. However, according to the foregoing embodiment, eachmovable rack has the small DC power supply circuit 160 which is light inweight and less expensive.

In a further modified example of the control circuit shown in FIG. 16, aDC power supply circuit is constituted by a solar panel 180 and asecondary cell 182 for storing power produced by the solar panel 180.The solar panel 180 includes a plurality of solar cell module groupswhich are juxtaposed in order to obtain a desired amount of output, andis positioned outdoors. Each solar cell module group is constituted bysolar cell modules connected in series. An output terminal of the solarpanel 180 is connected to the secondary cell 182 via a reverse blockingdiode 181 in order that the power produced by the solar panel 180 isstored in the secondary cell 182. The secondary cell 182 is used for themovable racks in order to activate the DC motors, the CPU 150 and so on(shown in FIG. 13).

The foregoing DC power supply may be applicable as a main or subsidiarypower supply for the movable racks in order to operate the movable rackswith reduced power.

A further embodiment of the invention will be described hereinafter. Inan example of FIG. 17, a power-assisted movable rack system comprisesfour movable racks 301 to 304, which have front and rear wheels 208 atthe bottoms thereof, and DC motors 351 to 354 for rotating the wheels208 which travel on rails on a floor.

The movable rack 301 includes right and left direction switches 311 and312. The movable racks 302 to 304 are provided with right and leftdirection switches 321, 322, 331, 332, 341 and 342, respectively. FIG.17 shows the side panels of the movable racks 301 to 304, and the rightdirection switches are positioned at the left sides of the side panelswhile the left direction switches are positioned at the right sides ofthe side panels. The direction switches 311, 321, 331 and 341 areoperated in order to move the movable racks 301 to 304 to the rightwhile the direction switches 312, 322, 332 and 342 are operated in orderto move the movable racks to the left.

An electric circuit provided in each movable rack will be described withreference to FIG. 18. It should be noted that FIG. 18 shows the electriccircuit of the movable rack 302 as an example. The electric circuits ofthe remaining movable racks are identical to this electric circuit. Theelectric circuit comprises: a control circuit 250 for controlling theforward and reverse rotations, stopping and braking of a DC motor 252,and being constituted by a micro-computer; and a DC stabilizing powersupply 253 for converting commercial AC power into DC 24V power andsupplying it to the control circuit 250. The control circuit 250 isconnected to the right and left direction switches 321 and 322, left andright frame safety bar switches 261 and 262, left and right work spacesafety bar switches 263 and 264, and an emergency state canceling switch265, all of which function as input means.

The left and right frame safety bar switches 261 and 262 are connectedto the safety bars attached on the left and right side surfaces of theframes of the movable rack 302. These switches 261 and 262 are operatedwhenever the safety bars come into contact with an operator or somethingwhile movable racks are being moved in order to form a new work space.

The left and right work space safety bar switches 263 and 264 areconnected to the safety bars attached on the left and right frontages ofone of rack shelves of the movable rack 302. Specifically, when theoperator strikes against the left or right safety bar in the work spacebeing formed, the left or right work space safety bar switch 263 or 264is selectively operated. In this state, all the movable racks madeimmovable regardless of the operation of any of the left or rightdirection switch. Further, the safety bar lamp 268 or 269 of the movablerack whose switch 263 or 264 has been operated is turned on in order toindicate that none of the movable racks can be moved.

In an emergency, the operator may intentionally touch any of theforegoing safety bars in order to stop the movable racks. In such acase, either the switch 263 or 264 is activated, thereby stopping themovable racks. The emergency state canceling switch 265 is operated inorder to return the emergently stopped movable racks to their originalstate, and make them movable.

The DC motor 352 and the right and left safety bar lamps 268 and 269 areconnected to the control circuit 250 as output members. The controlcircuit 250 rotates the DC motors 352 forward or backward while eitherthe rightward or leftward signal is being input, stops the DC motor 352when the leftward or rightward signal is terminated, and applies thedynamic braking to the DC motor 352. Further, the control circuit 250 isprovided with an actuating circuit for applying the dynamic braking tothe DC motor 352 in response to the emergency stop signal.

In response to the operation of the right direction switch 321, thecontrol circuit 250 of the movable rack 302 controls the actuatingcircuit, activates the DC motor 352 in order to move the movable rack302 to the right, and issues the rightward signal. The rightward signalis transmitted to the right movable rack 303 via a right rackcommunication line. When the left direction switch 322 is operated, thecontrol circuit 250 controls the actuating circuit, activates the DCmotor 352 in order to move the movable rack 302 to the left, and issuesthe leftward signal. The leftward signal is transmitted to the leftmovable rack 301 via a left rack communication line.

Further, in response to the leftward signal from the movable rack 303via a right communication line, the control circuit 250 of the movablerack 302 controls the actuating circuit, activates the DC motor 352 inorder to move the movable rack 302 to the left, and issues the leftwardsignal. The leftward signal is transmitted to the left movable rack 301via a left rack communication line. Still further, when receiving therightward signal from the movable rack 301, the control circuit 250 ofthe movable rack 302 controls the actuating circuit, activates the DCmotor 352 in order to move the movable rack 302 to the right, and issuesthe rightward signal, which is transmitted to the movable rack 303 via aright rack communication line.

The control circuit of each movable rack controls the actuating circuitin order to operate the DC motor of the movable rack at the rated outputwhen the right or left direction switch is operated thereon. Further,when a driven movable rack receives the rightward or leftward signalfrom a driving movable rack, the control circuit of the driven movablerack controls the actuating circuit in order that the DC motor of thedriven movable rack is operated by power which is smaller than that bywhich the driving movable rack is moved, or smaller than that by whichthe driven movable rack cannot move by itself. The rated output of eachDC motor is obtained by applying the 24V-8 A current while the power bywhich the driven movable rack cannot move by itself is obtained byapplying approximately 24V-6 A current.

The actuating circuit of each control circuit also includes a dynamicbraking force producing circuit for stopping the movable racks. FIG. 21shows an example of the braking force producing circuit for the movablerack 302. The actuating circuit provides power to terminals of the DCmotor 352 in order to rotate it forward or backward as described above.A switch 220 is provided via a 2 Ω resistor between the terminals of theDC motor 352 in order to short-circuit the terminals, and serves as oneof dynamic braking force generating circuits. Further, a switch 224 isprovided via a 4 Ω resistor between the terminals. The switches 220, 222and 224 are relay switches or thyristors which are turned on and off bythe control circuit 250.

The movable racks 301 to 304 include circuits which are identical tothose shown in FIGS. 18 and 21.

The operation of the foregoing embodiment will be described withreference to FIGS. 23 to 25. Referring to FIG. 25, it is checked by theoperator (step S21) whether or not the presence of a work space isindicated. If not, it is considered that no work is being carried outbetween the movable racks. It is checked (step S22) whether or notmovable racks can be moved without any problem. If not, either right orleft direction switch 321 or 322 is operated (step S23). In this state,the DC motor 352 is actuated and controlled, so that the movable rack302 is moved to the right or left (step S24), as will be described indetail later.

In this state, the operation of the safety device is checked (step S25),i.e. it is checked whether any one of the left and right frame safetybar switches 261 and 262 and the left and right work space safety barswitches 263 and 264 of the movable rack 302 is operated. If not, themovable rack 301 keeps on moving until the right or left directionswitch 321 or 322 is turned off (step S26), and is stopped when theforegoing switch is released, as the normal braking operation (step S27)(to be described in detail later). On the contrary, if the safety deviceis operated (step S28), the movable rack 301 is immediately stopped, aswill be described in detail later.

Referring to FIG. 23, when either the right or right direction switch isfound to be active (step S31), a current to be supplied to a DC motor ofthe movable rack whose switch has been turned on (this movable rackbeing called the “driving movable rack” is controlled in order toactuate the electric motor of the driving movable rack, e.g. an 8 Acurrent is supplied in this case (step S32). A 6 A current is introducedinto a driven movable rack (i.e. a “lower order movable rack” in a daisychain and called the “driven movable rack”) which is pushed by thedriving movable rack. This current is smaller than the current suppliedto the DC motor of the driving movable rack, e.g. a current which isslightly insufficient to move the driven movable rack. The DC motor ofthe driving movable rack is rotated forward or backward (step S34),thereby moving the driven movable rack which is right or left to thedriving movable rack.

In step S35, it is checked whether or not the driving movable rack hasmoved the driven movable rack. Power supplied to the DC motor of thedriven movable rack is turned off (step S38). Rotary force of the wheelsof the driving movable rack is transmitted to the electric motor of thewheels of the driven movable rack, so that the DC motor is rotated inorder to generate power (step S38). Both the driving and driven movableracks are actuated and moved for the predetermined distances, therebyforming the work space (step S36). The operator determines the timing toturn off the left or right direction switch, and inactivates the switch(step 39).

Power supplied to the driving movable rack is suspended, so that the DCmotor of the driven movable rack is stopped or those of a plurality ofdriven motors are stopped. In the driving movable rack, the terminals ofthe DC motor are connected via an appropriate resistor in order toregulate the generated current and apply the dynamic braking to the DCmotor (step S40). In the driven movable rack, the terminals of the DCmotor are connected via an appropriate resistor in order to regulate thegenerated current and apply the dynamic braking to the DC motor (stepS41). The remaining stationary movable racks which and have higherorders in the daisy chain are braked by regulating the current (stepS42). Actually speaking, no braking force is produced because no powerhas been produced. Usually, the movable racks are stopped by applyingbraking force by turning off the right or left direction switch, whichis called normal braking control.

The dynamic braking force varies with the sizes of articles stored inthe movable racks, so that the movable racks can be stopped within asubstantially constant distance even if articles loaded therein vary. Inother words, the larger the load, the larger the inertia force, the morepower is generated, and the larger the dynamic braking force.Conversely, the smaller the load, the smaller the inertia force, and thesmaller the generated power and the dynamic braking force.

When the dynamic braking is applied, the movable racks are immediatelystopped. Thereafter, the motor terminals are shorted for approximately0.1 second to 1.0 second in order to maintain the braked state (stepS43). During the dynamic braking, no current is applied to the DCmotors. Thereafter, the foregoing state will be canceled, and the DCmotors may become ready, so that the movable rack system will becomeready for a next operation.

The emergency braking control will be described with reference to FIG.24. In FIG. 24, steps S51 to S54 are identical to the steps S31 to S35shown in FIG. 23. Further, steps S56 and S57 in FIG. 24 are identical tothe steps S37 and S38 in FIG. 23. It is assumed here that one drivingmovable rack pushes a plurality of driven movable racks. It is checkedin step S55 whether or not the safety device is active, i.e. whether ornot the left or right frame safety bar switch 261 or 262, or the left orright work space safety bar switch 263 or 264 is active. If the safetydevice is found to be active, either the left or right safety devicelamp 268 or 269 is turned on. Otherwise, one of the direction switchesremains depressed. When a work space of a desired size is completed(step S62), the direction switch is turned off (step S63) in order tostop the movable racks (step S64) as described previously.

If the safety device is found active in step S55, the correspondingsafety device lamp 268 or 269 blinks in order to indicate the activationof the safety device (step S58), and dynamic braking is applied to themovable racks without regulating the power generated by the DC motors(step S59). Since the emergency stop signal has been issued in thiscase, the switch 220 (shown in FIG. 21) is turned on, the terminals ofthe DC motors 352 are shorted, and the DC motors are inactivated usingmaximum dynamic braking force, which stop not only the driving movablerack but also the driven movable racks. Further, dynamic braking will beapplied to the stationary movable racks, i.e. higher order movable racksin the daisy chain (step S60).

The succeeding operation is identical to the operation for which thenormal dynamic braking is applied. In response to the dynamic braking,all the movable racks are promptly stopped. Thereafter, the motorterminals remain shorted for 0.1 second to 1.0 second, i.e. the dynamicbraking is maintained (step S61). Then, this state is canceled, the DCmotors become ready, and a series of operations is completed forpreparation of the succeeding operation.

In the foregoing embodiments, the dynamic braking is applied to the DCmotors when movable racks should be stopped. Movable racks filled withheavy articles can be stopped in short stopping distances. Therefore,the movable racks can stop moving in a relatively uniform stoppingdistance and with relatively equal spaces maintained therebetween.

FIG. 26 shows the comparison between stopping distances required for thedynamic braking, and stopping distances required for braking movableracks using AC motors as a driving source in the related art. Line arepresents a stopping distance when the dynamic braking is applied via a2 Ω resistor with terminals of a DC motor shorted, line b represents astopping distance when the dynamic braking is applied via a 3 Ω resistorwith the terminals of the DC motor shorted, and line c represents astopping distance when the dynamic braking is applied via a 4 Ω resistorwith the terminals of the DC motor shorted. Line d represents a stoppingdistance required for braking movable racks using AC motors in therelated art. As can be clearly understood on the basis of line d, thestopping distance is long in the related art compared with the presentinvention. Further, the heavier the load on a movable rack, the longerthe stopping distance. With the present invention in which the dynamicbraking is applied to the DC motors, the stopping distances areincreased according to weight of load but are relatively short as awhole. In other words, the stopping distances do not usually depend uponthe weight of load. Needless to say, the smaller the space between motorterminals, the larger the dynamic braking force, which is effective inreducing the stopping distances.

According to the invention, the dynamic braking is applicable to drivenmovable racks which are pushed by the driving movable rack. As a result,the power-assisted movable racks can be stopped quickly withsubstantially equal spaces maintained therebetween.

In the foregoing embodiments, the DC motors of the power-assistedmovable racks are rotated forward or backward in response to theoperation of the right or left direction switch. The right and leftdirection switches should be easily operated only when necessary, butshould be prevented from being incidentally operated. FIGS. 19 and 20show right and left direction switches 321 and 312 which are designed inorder to meet the foregoing requirements.

Referring to FIGS. 19 and 20, the movable racks 301 and 302 arepositioned side by side and have notches 371 and 372 on their sidepanels 361 and 362, respectively. Switch panels 381 and 382 are fittedin the notches 371 and 372, and are not flush with the frontages of themovable 301 and 302 but are inclined by approximately 15 degrees. Theright and left direction switches 312 and 321 are attached on the switchpanels 381 and 382, respectively, are inclined with respect to thefrontages, and can be easily operated. Further, the right and leftdirection switches 312 and 321 do not project out of the side panels 361and 362. Therefore, these direction switches 312 and 321 are preventedfrom being incidentally operated.

Further, the right and left direction switches 312 and 321 are fitted inthe notches 371 and 372, and are back from the frontages of the movableracks 301 and 302. Therefore, even when the movable racks 301 and 302are close to each other, the right and left direction switches 312 and321 can be operated via a gap present therebetween.

The right and left direction switches 312 and 321 may be inclined by 0degrees to 75 degrees, preferably by 10 degrees to 45 degrees, withrespect to the frontages of the movable racks 301 and 302. Further,these switches may be preferably positioned at a level of 1000 mm, andmay be 300 mm to 1800 mm, from the floor.

The invention is advantageous in that the power-assisted movable racksystem can reduce stopping distances and maintain substantially equalspaces between the movable racks. However, the power-assisted movableracks themselves should be mechanically structured in order to maintainsubstantially equal spaces therebetween. For instance, a movable rackmay be twisted and lean to the right or left because the wheels may turnat different speeds due to non-uniform load or some mechanical problem.A space may be enlarged between an adjacent movable rack and such amovable rack when it is stopped.

In order to overcome this problem, wheels of the movable rack areattached to a frame, and are coupled using shafts. A power transmissionis positioned at the center of at least one of the shafts, as shown inFIG. 22.

Referring to FIG. 22, a frame of one movable rack includes one pair eachof front and rear wheels 208 along the moving direction of the movablerack. The front wheels 208 are coupled by a rotary shaft 230 while therear wheels 208 are coupled by a rotary shaft 231. In other words, thewheels 208 are present at the opposite ends of the rotary shafts 230 and231. The rotary shafts 230 and 231 are rotatably supported by aplurality of bearings 234 which are attached to beams constituting theframe. A gear 233 as the power transmission is disposed at the center ofthe rotary shaft 230 extending between the wheels 208. The gear 233 isengaged with a small gear 232 fixedly attached to an output shaft of aDC mo tor 252. Alternatively, the power transmission may be constitutedby a chain and sprocket, a worm and a worm wheel, or the like.

With the foregoing structure, the wheels 208 are substantially equallyspaced from the power transmission at the center of the shaft 230.Therefore, when power is transmitted from the DC motor 252 to the shaft230, the shaft 230 is equally twisted at the opposite ends thereof, sothat the movable rack can move smoothly and in a balanced state on therails without leaning, and can have a uniform space from an adjacentmovable rack.

Needless to say, the driven wheels 208 (shown at the lower side in FIG.22) are not always required to be coupled using a continuous shaft(correspond to the shaft 231 in FIG. 22).

The structure shown in FIG. 22 is applicable to all of the movable racksconstituting the movable rack system.

INDUSTRIAL APPLICABILITY

According to the invention, the power-assisted movable rack systemcomprises a plurality of movable racks. Each of the movable racksincludes, a plurality of wheels, the DC motor turning forward orbackward and reciprocating the movable rack, a pair of directionswitches provided at opposite positions in moving directions of themovable rack, and the actuating circuit rotating the DC motor in onedirection during the operation of one of the direction switches androtating the DC motor in an opposite direction during the operation ofthe other direction switch.

An operator can move movable racks in opposite directions by operatingdirection switches as he or she desires.

The DC motor functioning as a drive source has a maximum start torqueand can activate movable racks without increasing a speed reductionratio, so that movable racks can be moved at a high speed. Further, theDC motor can apply maximum dynamic braking to movable racks, whichenables the movable racks to stop with a short braking distance.

In a movable rack where either the left or right direction switch isoperated, the DC motor associated with the operated switch is actuatedin order to move the movable rack (functioning as a driving movablerack) to the left or right. A movable rack which is left or right to thedriving movable rack is also moved. Power which is smaller than thatapplied to the driving movable rack is applied to the movable rack movedby the driving movable rack, so that running torque is generated in themovable rack moved by the driving movable rack. This is effective inreducing loads applied to the DC motor functioning as a drive source.

1. A power-assisted movable rack system comprising a plurality ofmovable racks, each movable rack including: a plurality of wheels; a DCmotor turning configured to turn forward or backward and to reciprocatethe movable rack; a pair of direction switches provided at oppositepositions of a side panel in moving directions of the movable rack; andan actuating circuit and a power source configured to rotate the DCmotor in one direction during operation of one of the direction switchesand to rotate the DC motor in an opposite direction during operation ofthe other direction switch, wherein the plurality of movable racks arejuxtaposed and each movable rack is configured to move other movableracks.
 2. A power-assisted movable rack system comprising a plurality ofmovable racks, each movable rack including: a plurality of wheels; a DCmotor configured to turn forward or backward and to reciprocate themovable rack; a direction switch provided on the movable rack and pushedto a direction in which the movable rack is moved; and an actuatingcircuit and a power source configured to rotate the DC motor in onedirection during operation of the direction switch and to rotate the DCmotor in an opposite direction during operation of the direction switchin the other direction, wherein the plurality of movable racks arejuxtaposed, and each movable rack is configured to move other movableracks.
 3. The movable rack system of claim 1, wherein the actuatingcircuit enables the movable racks to move simultaneously in oppositedirections and are separated from each other while direction switches ofadjacent movable racks are simultaneously operated.
 4. The movable racksystem of claim 1, further comprising a safety device configured todetect an emergency and to issue an emergency stop signal so thatmaximum dynamic braking is applied to the DC motor.
 5. The movable racksystem of claim 2, further comprising a safety device configured todetect an emergency and to issue an emergency stop signal so thatmaximum dynamic braking is applied to the DC motor.